Private repairman for OMNI VI

I am pulling my hair out. I have just received my OMNI VI back from
Tentec factory service for the second time in the last 6 weeks, and all I
get is implausible excuses why they cannot remove the ringing/howling
from my 500Hz and 250Hz filters. First they "aligned" everything. Then
they sent me a repalcement 500Hz filter, which I installed, to worse
result than the original re ringing/howling. Then they told me I had the
wrong firmware, because my S/N OMNI VI needed a special version of the
firmware because the basic 2.4MHz filter was not zeroed in, and needed
software offset to make the optional filters (500/250) track. They
changed the firmware and "re-aligned" everything, then told me the
problem was the G4PKT higher order product detector I had installed.
I told them it couldn't be, because the filter ringing/howling had occurred
from the time I got the OMNI three years ago. Anyway, they pulled out the
IF board with the add-on product detector, put in their stock IF board--
and voila, the 500Hz/250Hz filters ring WORSE than ever!
Does anyone out there in Tentec reflectorland know of a private repair
person, knowledgeable and skilled in Tentec equipment, who can get the
OMNI VI straightened out for me?
73, Larry N6AZE, 6E2T